Toxins produced by microbial agents, for example bacteria, can be used as antigens in the process of active immunisation, where the production of antibodies is stimulated by the introduction of a specific antigen. Frequently, the toxin must be inactivated so that it can be administered safely, while at the same time its antigenic effect must be maintained. An inactivated toxin, known as toxoid, is commonly prepared from various microorganisms by the addition of formaldehyde. Another compound used for this purpose is tannic acid, obtained from fermented oak galls.
The manufacture of toxoids and vaccines involves very close quality control and the products require special handling and storage. Legislation has been passed in many countries controlling the manufacture, storage and use of vaccines in order to ensure the maximum safety.
Nevertheless, biological preparations of this type exhibit various side-effects which are unavoidable even under strict control. For instance, pertussis vaccine, which is epidemiologically regarded as a necessity, especially in developing areas such as South East Asia and Africa, is known to produce side-effects such as swelling at the inoculation site, pain, systemic fever, vomitting and also symptoms of shock or, occasionally, serious brain damage. There is thus a real need for a method which will eradicate the unpleasant side-effects of such a vaccine, while at the same time the prophylactic effect is maintained.